The basic question which this proposal addresses is that of the mechanisms by whci programmed gene expression results in the achievement of differentiated morphology. Tubulin, like actin, collagen, hemoglobin, and many other proteins of central importance to eucaryotic organisms, exists in a number of related byt separately encoded froms. We propose to study the relationship of the tissue- or time specific appearance of different tubulin subunits to the specificity of microtubule function during embryogeneris in Drosophila melanogaster. We have characterized three tubulin subunits which are synthesized throughout development. In addition, we have identified another tubulin subunit which is solely a product of the zygotic genome and is expresses only during a brief period in mid-empryogenesis, at a time when extensive morphogenesis takes place, including neurogenesis and the beginning of organogenesis. Our objective is to define the time of appearance, localization in the embryo, functional role of the embnryonic tubulkins, and to examine the contribution of maternally derived inofrmation stored in the egg versus the contribution of the zygotic genome. We will combine genetic analysis with biochemical studies: 1) We will define the tissue specificity of the embryonic tubulins by analysis of known mutations in which the identity of cells in certain regions of the embryo is changed. 2) We will isolate and characterize mutations in the structural genes for the embryonic tubulins in order to determine the function of the wild-type gene products in development . 3) We will use cloned DNA sequences specific to different tubulin genes as pro es for tubulin gene expression at the level of RNA. 4) We will isolate monoclonal antibodies specific for different tubulin subunits. Such specific antibodies would constritute a powerful means for determining the localization of tubulin sunbunits within the embryo, for localizing different forms of tubulin within the same cell, and for analyzing functional specificities of the subunits at the level of protein structure